linshenkx/prompt-optimizer · error · EvaluationValidationError

${label} label must not be empty.

Error message

${label} label must not be empty.

What it means

Every content block (e.g. a test case input) must itself carry a non-empty label so runs and results can be identified. validateContentBlock throws when the block exists but block.label is missing or whitespace-only.

Source

Thrown at packages/core/src/services/evaluation/service.ts:1700

      }

      if (assetId && b64) {
        throw new EvaluationValidationError(
          `${label} #${index + 1} must not provide both assetId and b64.`
        );
      }
    });
  }

  private validateContentBlock(
    block: EvaluationContentBlock | undefined,
    label: string
  ): void {
    if (!block) {
      throw new EvaluationValidationError(`${label} must not be empty.`);
    }
    if (!block.label?.trim()) {
      throw new EvaluationValidationError(`${label} label must not be empty.`);
    }
    const hasContent = !!block.content?.trim();
    const hasMedia = this.hasBlockMedia(block);
    if (!hasContent && !hasMedia) {
      throw new EvaluationValidationError(`${label} content must not be empty.`);
    }
    if (block.media) {
      this.validateMediaItems(block.media, `${label} media`);
    }
  }

  private validateTestCase(testCase: EvaluationTestCase | undefined, label: string): void {
    if (!testCase?.id?.trim()) {
      throw new EvaluationValidationError(`${label} id must not be empty.`);
    }
    this.validateContentBlock(testCase.input, `${label} input`);
  }

View on GitHub (pinned to 3e677b1d9f)

Solutions

1. Add a descriptive non-empty label to the content block named in the message
2. Use the error's block label to locate the exact failing block in your payload
3. Add a client-side lint over evaluation payloads before submission

Example fix

// before
input: { content: 'Translate this' }

// after
input: { label: 'translation prompt', content: 'Translate this' }

function assertBlockLabels(blocks: { label?: string }[]): void {
  blocks.forEach((b, i) => {
    if (!b?.label?.trim()) throw new Error(`block[${i}] missing label`);
  });
}

const hasBlockLabel = (b: { label?: string } | undefined): boolean => !!b?.label?.trim();

try {
  await evaluationService.create(request);
} catch (err) {
  if (err instanceof EvaluationValidationError && /label must not be empty/.test(err.message)) {
    promptUserForLabel(err.message);
  } else throw err;
}

When it happens

Trigger: A content block like { content: 'hello' } with no label, or label: ' '. The label placeholder in the message identifies which block (e.g. 'Test case #1 input').

Common situations: Copy-pasted payloads with label stripped; programmatic test-case generation that only sets content; localization/import tooling leaving labels blank.

Understand the failure class

Background: Schema validation failed / invalid input schema: payload rejected because its shape doesn't match the expected schema — this error's family across 28 libraries.

Related errors

• ${label} #${index + 1} label must not be empty.
• ${label} must not be empty.
• ${label} content must not be empty.
• Result evaluation snapshot testCaseId must match testCase.id
• Image result evaluation requires at least one output image e

AI-assisted analysis of linshenkx/prompt-optimizer@3e677b1d9f (2026-08-27). Data as JSON: /api/errors/90b40ef8cbb280ec. Report an issue: GitHub.